From German Patent Publication No. DE 10 2005 015479 A1 it is known to bypass an SCR catalytic converter (SCR=selective catalytic reduction) by means of a bypass line in order to keep the temperature of the exhaust gases flowing through the catalytic converter within a certain range.
French Patent Publication No. FR 2 914 947 A1 discloses an internal combustion engine with an exhaust gas line containing an SCR catalytic converter where a bypass line controlled by a control element is provided for bypassing the SCR catalytic converter.
German Patent Publication No. DE 44 21 257 A1 discloses an internal combustion engine with two groups of cylinders, which can be switched off individually, each group having its own exhaust gas catalytic converter. In order to avoid cooling of the catalytic converter below its operating temperature when the corresponding cylinder is switched off, the entire exhaust gas line is designed in such a way that the gases expelled from the switched-off cylinder group are heated by the exhaust gases of the active cylinder group. No bypass line is provided for bypassing the catalytic converters.
Furthermore there is known from European Patent Publication No. EP 0 580 931 A1 an internal combustion engine with a bypassable start-up catalytic converter, wherein for reliable and fast switching between a cold-operation state in which the start-up catalytic converter is activated and a hot-operation state in which the start-up catalytic converter is bypassed, the control element is configured as a slideable annular exhaust gas sleeve, which can slide along and is coaxial with the exhaust gas line.
Especially in the case of large multi-fuel marine engines the quality of the exhaust gas is strongly dependent on the fuel used. In order to comply with severe exhaust gas regulations in coastal waters, among other measures SCR catalytic converters are used in marine engines for the reduction of nitrous gases. To avoid contamination and destruction of the SCR catalytic converter when the engine is running on heavy fuel oil the SCR converter can be bypassed by means of a bypass line. External bypass lines, however, have the disadvantage of substantially increasing the space required for the engine. As a further drawback the deactivated SCR converter will cool to below minimum operating temperature.